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In a world full of competing claims about products, diets, books, and supplements, it’s hard to sort out what’s true and what’s false about nutrition. But here are a few common nutritional myths that should be permanently retired, with some facts to remember:

You can lose lots of weight fast, and keep it off with the latest fad diet. Wouldn’t that be nice? Fad diets may work in the short term, but they’re hard to follow for very long. And over time, almost everyone who takes off pounds with the all-cabbage soup diet (or the grapefruit diet, or the fill-in-the-blank diet) gains it back. Plus, drastically restricting your calorie intake and/or certain types of foods isn’t healthy.

Eat lots of low-fat and fat-free foods to lose weight. Just because a product is “low-fat” doesn’t mean it is low in calories. In fact, many “low-fat” foods can have more calories, from ingredients like sugars. If you want to lose weight, burn more calories than you take in.

Some foods actually burn calories. Keep in mind that while foods themselves don't burn calories, some foods are credited with helping you lose weight because of the substances in them that increase how efficiently you burn energy. Calcium in people who are calcium-deficient may help weight loss. Caffeine, green tea, and capsaicin, a substance found in hot chili peppers, are thought to help your body burn more calories by increasing metabolic rate.

Fresh vegetables are more nutritious than frozen. Fresh produce may actually lose some of its nutrients as it is exposed to light and air, while vegetables and fruits that are frozen immediately after harvest can hold more of their valuable nutritional content.

If some of a vitamin or supplement is good, then more is better. Not necessarily. Megadoses of certain vitamins or supplements can cause more health problems than they help. While some people may need a multivitamin or a specific supplement due to particular health needs, the best way to get your nutrients is from the foods you eat. Talk to your doctor before starting a vitamin or supplement.

If a product is all-natural, then it’s safe. Not always. Just because a supplement is called "natural" doesn’t mean it is safe if you don’t follow directions. The content of many of these supplements are not regulated by the Food and Drug Administration, so it’s hard to know the exact ingredients in a particular supplement, or how much of any ingredient is in there.

When choosing a dietary supplement, look for the USP Verified Mark that assures consumers that a supplement has passed a stringent testing and evaluation process by the U.S. Pharmacopeia (USP). The USP is a nonprofit scientific testing organization that sets standards for the quality, purity, identity, and strength for medicines, dietary supplements, and food ingredients.

As always, be sure to check with a doctor about the ingredients in any vitamin or supplement product before taking it.